An anemometer is generally understood to be a device for measuring wind speed. An anemometer may include a rotor with radially extending blades and/or cups for catching wind or other fluid flow which, in turn, may cause the rotor to spin about an axis. Wind speed or fluid flow rate may be directly proportional to the revolutions of the rotor in a given period of time, and a pickup device, such as a transducer, coupled to the rotor may convert the rotational speed of the rotor into a corresponding electrical output signal proportional to wind speed or fluid flow rate.
An anemometer may further include a bearing assembly for allowing the rotor to freely spin about an axis. However, bearing assemblies may be susceptible to degradation from impact loads and/or contamination from debris and other particulate matter. For example, in the field, anemometers, including the bearing assemblies, may be exposed to various forms of debris and contaminants carried by the wind and may further be subject to impact loads due to structure ice shedding and/or weather precipitation, such as rain, snow, hail, sleet, etc.
Current anemometers may be arranged in such a way that air exchange occurring through the anemometer may also occur through the bearing assembly, thereby exposing the bearing assembly to debris and contaminants. For example, some current anemometers include a single shaft about which the rotor may rotate. However, the bearing assembly for allowing the single shaft to rotate may be exposed to incoming debris carried with the air.
Some anemometers may include mechanical seals in an attempt to prevent exposure of the bearing assembly to contaminants and weather-related events. In particular, some anemometers may include a labyrinth seal within the bearing assembly to reduce airflow and further trap particulates in the labyrinth seal, rather than relying on the bearing assembly, for example.
A bearing assembly having a labyrinth seal may have drawbacks. For example, a bearing assembly including a labyrinth seal may still allow air and small debris, such as corrosive pollutants and abrasive dust, to pass through the assembly. In particular, a basic flaw in a labyrinth seal design is that air exchange still occurs inside the sensor and must pass through the bearings due in part to the single-shaft design of the anemometer. In order to compensate for any water that may pass into the air exchange, anemometers having a labyrinth seal may further include drain holes for allowing water to pass through the labyrinth seal and drain. The drain holes may improve airflow through the anemometer, thereby further exposing the bearings to debris. Additionally, in order for a labyrinth seal to properly function as intended, it may be required that the dimensional clearances and/or manufacturing tolerances of the bearing assembly be relatively tight and restrictive.
Some anemometers may also include bearing assemblies wherein the rolling elements, such as ball bearings, may be sealed. As generally understood, sealed bearings may be formed by creating a seal contacting and engaging both inner and outer races of the bearing, thereby sealing the rolling elements. However, although sealed bearings may function to prevent debris from entering the bearing, the structure of a sealed bearing may result in higher amounts of friction, thereby causing relatively inaccurate and poor interpretation of the wind direction and/or speed by the anemometer.